This invention of the present disclosure is related to ultrasonic welding mounts, and particularly to system, apparatus and method for mounting an ultrasonic horn having a predetermined resonant frequency with a mount having about the same resonant frequency.
Ultrasonic welding is typically used to join multiple parts together using vibrations converted into heat energy. Common types of ultrasonic welding are plunge and continuous welding, for example, scan or rotary welding. In plunge welding, an ultrasonic horn plunges (travels towards the parts) and transmits vibrations into a top part. In continuous welding, the ultrasonic horn is typically stationary or rotating and the part is moved beneath it. Continuous ultrasonic welding is typically used for sealing fabrics, films, and other parts. Scan welding is a type of continuous welding in which the part moves. The plastic part is scanned beneath one or more stationary horns. Each of the ultrasonic welding types involves a horn.
All horns impart energy to the parts to be welded at a selected wavelength, frequency, and amplitude. A rotary horn includes a shaft with input and output ends, and a welding portion mounted on and coaxial with the output end. The diameter of the welding portion is typically greater than the diameter of the shaft. The welding portion has a cylindrical weld face having a diameter that expands and contracts with the application of vibration energy. Typically, a rotary horn is cylindrical and rotates about a longitudinal axis. The input vibration is in the axial direction and the output vibration is in the radial direction. The horn and anvil are close to each other, and the anvil can rotate in the opposite direction of the horn. The part (or parts) to be welded passes between the cylindrical surfaces at a linear velocity, equal to the tangential velocity of the cylindrical surfaces. Matching the tangential velocities of the horn and the anvil with the linear velocity of the material is tends to minimize the drag between the horn and the material.
Typically, two methods are used to mount an ultrasonic horn: nodal mounting and non-nodal mounting. A node is a position of the horn that has zero displacement in one or more directions. As used with respect to horns in this application, a node is a point or region on an ultrasonic horn where the longitudinal displacement is negligible or zero and the radial displacement is at or near its maximum when the horn is in resonance. An anti-node is a point or region where the longitudinal displacement is at or near its maximum and the radial displacement is at or near its minimum.
With a nodal mount, the horn can be held or grasped rigidly. One type of non-nodal mount is used at an anti-node of the horn. Anti-nodes are areas of maximum longitudinal displacement of the horn (or other component, such as a booster). Attaching mounting systems at a non-nodal location, such as the anti-node, requires the mount to be designed to isolate the vibration from the horn. Non-nodal mounts typically require some flexible elements because the horn surface is moving (vibrating) at the point where the mount is located.
One aspect of the present disclosure is directed to a system for ultrasonic manufacturing. The system includes a horn having a resonance at a predetermined frequency and a mounting member having a resonance at about the same predetermined frequency. The mounting member is coupled to the horn at a point where the horn has an anti-node at the predetermined frequency. In one example embodiment, the horn is a rotary horn. In another example embodiment, the system includes a base element, a pair of flanges extending outwardly from the base element, and a mount element extending inwardly from the base element.
Another aspect of the present disclosure is directed to a mounting member for an ultrasonic horn. The mounting member includes a base element and a pair of flanges extending outwardly from the base element and defining an exterior bearing surface. The mounting member also includes a mount element extending inwardly from the base element and defining an interior bearing surface. The exterior bearing surface is a node when the interior bearing surface is driven at a predetermined frequency. In one example embodiment, the motion of the exterior bearing surface is less than two percent of the motion of the interior bearing surface when the mount element is driven at the predetermined frequency. In another example embodiment, the mounting member has a resonant frequency of about 20,000 Hertz. In another example embodiment, the mounting member has a resonant frequency of about 40,000 Hertz. In another example embodiment, the mounting member is of a unitary construction.
Another aspect of the present disclosure is directed to a method of mounting an ultrasonic horn. The method includes providing a horn having a resonance at a predetermined frequency and attaching a mount having a resonance at about said predetermined frequency to the horn at a point where the horn has a node at the predetermined frequency. In one embodiment, the horn is a rotary horn.